Fig. 4: Movement directions of calling birds and reactions of flock mates.
a,b, Movement directions of a calling bird within 209 ms following the onset of stack calls showed a significant (Rayleigh test, P = 0.018, z = 3.99, n = 93) directionality in the horizontal/vertical plane (a), but not (Rayleigh test, P = 0.277, z = 1.29, n = 73) in the horizontal/wind direction plane (b). Light green circles and fans: individual movement directions and counts, respectively; dark green line: median movement direction. c–e, Box plots of flock mates’ spatial positions relative to a focal bird’s spatial position at the onset of 46 stack calls (blue) and at the time of initiation of 579 call-unaccompanied upwards movements (cyan). Dots: individual data points; boxes: 25th and 75th percentiles of distributions; horizontal lines: medians. LMM, estimates ± s.e.m.: 80.5 ± 19.9, P < 0.001, t = 4.04 (c); −127.2 ± 12.5, P < 0.001, t = 10.17 (d); 105.5 ± 37.9, P = 0.005, t = 2.78 (e). Sample sizes in c and d as in f, sample sizes in e as in g. f,g, Call-accompanied upwards movements caused flock mates to significantly reduce movement activity in the horizontal/vertical (LMM, estimates ± SE: 20.6 ± 4.9, p < 0.001, t = 4.2, n = 230; f) and the horizontal/wind direction plane (LMM, estimates ± s.e.m.: 52.3 ± 10.2, P < 0.001, t = 5.2, n = 202; g). Box plots show distances travelled by flock mates within 209 ms following the initiation of 46 call-accompanied (blue) and 535 call-unaccompanied upwards movements (cyan). Dots: individual data points; boxes: 25th and 75th percentiles of distributions; horizontal lines: medians; P values of LMMs are indicated. h–k, Movement directions of upwards-moving birds’ flock mates within 209 ms after call onset (h and i; Rayleigh test, P = 0.001, z = 7.13, n = 230, and P = 0.036, z = 3.31, n = 202, respectively) differ from movement directions of upwards-moving birds’ flock mates within 209 ms after initiation of call-unaccompanied upwards movements (j and k; Rayleigh test, P < 0.001, z = 27.43, n = 2,637, and P < 0.001, z = 15.05, n = 2,284, respectively). Light blue and light cyan circles and fans: individual movement directions and counts, respectively; dark blue and dark cyan lines: median movement direction.
